1. Field of the Invention
The present invention relates to a method of producing a ceramic multi-layer substrate on which semiconductor devices, chip capacitors, and other suitable components are to be mounted.
2. Description of the Related Art
In the production of ceramic multi-layer substrates on which semiconductor devices, chip capacitors, and other suitable components are to be mounted, ceramic green sheets are laminated to each other to form an unfired ceramic laminate, and then, the laminate is fired. However, when the unfired laminate is fired, the unfired ceramic laminate shrinks during firing, such that dimensional errors are caused.
Thus, for example, as described in Japanese Unexamined Patent Application Publication No. 4-243978, shrink-prevention ceramic green sheets, which are not sintered at the firing temperature of the unfired ceramic laminate, are arranged on both of the main surfaces of the unfired ceramic laminate, and the unfired ceramic laminate is fired at a temperature which is higher than the sintering temperature of the unfired ceramic laminate and which is lower than the sintering temperature of the shrink-prevention ceramic green sheets, and thereafter, the shrink-prevention green sheets are removed.
The specific method of removing shrink-prevention ceramic green sheets described in WO99/56510 is known, in which as a first method, spraying ceramic powder together with compressed air, as a second method, spraying water together with compressed air, and as a third method, spraying a mixture of ceramic power with water together with compressed air are described.
However, when the first, second, and third methods are individually used, the following problems occur.
That is, according to the first method, the removing capacity is low, since the spraying area of the ceramic powder is small. Also, the positional accuracy in the processing range is low. Thus, the processing may become unstable. As a result, it is difficult to uniformly remove the shrink-prevention ceramic green sheets. Moreover, a large-scale apparatus is required to collect the sprayed ceramic powder and the powder of the removed ceramic green sheets. Thus, expensive large-scale facilities are required.
According to the second method, a larger portion of the shrink-prevention ceramic green sheets can be removed. However, in the following situations, the shrink-prevention ceramic green sheets can not be removed. That is, if glass is included in the unfired ceramic laminate, the glass component of the unfired ceramic laminate and the ceramic component of the shrink-prevention ceramic green sheets will bond to each other to form a reaction layer. This reaction layer cannot be sufficiently removed simply by spraying water together with compressed air.
According to the third method, the shrink-prevention green sheets can be removed more uniformly as compared to the method of spraying ceramic powder together with compressed air. The removal-capacity is increased as compared to the method of spraying water with compressed air. However, according to this method, to allow re-use of the spraying ceramic powder, the ceramic powder to be sprayed must have an average particle size substantially equal to that of the ceramic powder of the shrink-prevention ceramic green sheets. If the particle size of the spraying ceramic powder is larger than that of the ceramic powder of the shrink-prevention ceramic green sheets, it will be difficult to remove the powder of the shrink-prevention ceramic sheets using a filter, and thus, the average particle size of the spraying ceramic powder changes as the time that the spraying ceramic powder is used increases. As a result, the removing conditions for the shrink-prevention ceramic sheets change, and thus, it is difficult to uniformly perform the processing. On the other hand, if the average particle size of the spraying ceramic powder is smaller than that of the shrink-prevention ceramic sheets, the shrink-prevention ceramic sheets can be removed using a filter. However, in the case in which the average particle sizes of the used ceramic powders are not significantly different from each other, a portion of the spraying ceramic powder will also be removed by the filter. Thus, the average particle size of the spraying ceramic powder changes as the time that the spraying ceramic powder is used increases. As a result, the removing conditions for the shrink-prevention ceramic sheets change. Thus, it is difficult to uniformly perform the processing.